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Flywheel on a rotary phase convertor
On Wed, 4 Jan 2006 13:20:04 -0600, "Robert Swinney"
wrote: Well, Don - you've missed the point again! What part of "2 induction motors operating from single phase current in a RPC configuration cannot be in parallel" did you fail to understand. The part that disagrees with an acknowledged authority, Mr. Hanrahan: http://www.metalwebnews.com/howto/ph-conv/fig1.html Your well intentioned, and colorful, drawings were not of a RPC configuration. Draw out a RPC and I think you may understand. I did. So did Hanrahan. His are in parallel. http://www.metalwebnews.com/howto/ph-conv/fig1.html Oh! be sure to include some capacitors. He did. They (in electronic terms) might be considered as steering capacitors, for it is their job to force the convoluted currents to flow in such a way as to *emulate* true 3-phase. Note, I said *emulate* because current flow in a RPC is not the same as current flow in parallel connected 3-phase motors, no matter which transform is used. Convoluted currents? Yeesh! RPC's aren't witchcraft and wizardry, mesh currents are mesh currents. The (parallel) caps provide some phase correction and resonant voltage boost to compensate for the reversal in I-Z drop because the third leg of the idler is a driving leg rather than a driven leg. They are not essential to the operation of an RPC, though they can improve balance. My RPC has no capacitors, starts and plug-reverses my lathe and mill just fine. |
Flywheel on a rotary phase convertor
The key point here is: "How my phase converter is wired when it runs a load
motor". The flawed logic is that a phase converter does not "run" a load motor. Such a differentiation between phase converter and load motor is not possible. An idler motor and load motor, taken together as a network, are what constitutes a rotary phase converter. This all harks back to the misunderstood "generator" concept as applied to an idler motor. The two must work together to form a rotary phase converter. Remember a RPC (the whole RPC) acts to manipulate current flow in a network so that the load motor voltages, and currents, are the same as if the load motor was operating from a 3-phase source. Remembering, all the while, the whole thing is running on *single-phase* current. Now as for parallel connectivity: The drawing is that of a classic RPC (idler and load motor) operating from Hot 1 and Hot 2, both sides of a single-phase source. Consider Hot 1. It connects to L1 of the idler motor and also to L1 of the load motor. The same can be said for Hot 2 and the 2 respective L2's. By definition, the points designated as L1 and L2 in both idler and load are operated in parallel across the line. That is to say the 2 main windings, L1 to L2 in your drawing of both idler and load are connected in parallel across the line. Now look at the way current flows in the L3 lead. The idler's L3 wire has 1 end connected to the 3rd. winding on the idler, call that a source point for L3 current flow. The other end of wire L3 connects not to the analogous same start point on the load motor but to a point on the other end of the load motor's L3. This is not, can not, be considered a parallel connection. The only way the two 3-phase motors could be connected in parallel is if they are both fed from a 3-phase source. In a manner of speaking, for a RPC (network) to do its thing, when taking in *single-phase* current and delivering *3-phase current* to a load motor (also part of the network) there has to be current flow in 2 directions the 3rd leg. Of course, aggregate current flow is such that current will flow in the "right" direction in the load motor's 3rd leg. Parts of the RPC act as both generators and consumers, thus the heavier element will cause current to flow, seemingly backwards, into the other element. And so it is with the RPC - capacitor augmentation can enhance the convoluted current flow in such a way as to make emulated 3-phase current flow in the load motor. Bob Swinney "Ignoramus18299" wrote in message .. . Here's how my phase converter is wired when it runs a load motor: idler Load L3-------------------------L3 / \ / \ L1 --- L2 L1---L2 | | | | | +------------------------+ +-----------------------------+ Hot2 Hot1 L1 connected to L1, L2 connected to L2, L3 connected to L3. L1 and L2 are also connected to utility power Hot1 and Hot2. How are these motors not running in parallel? They are. Leg numbering on the load motor is somewhat arbitrary, but however these motors are connected, the poles are connected in parallel. Maybe you have a different definition of "connected in parallel". My definition is that potential between like points (L1 to L1, L2 to L2, L3 to L3) is zero. Current does flow from L3 of one motor to L3 of another. i (now I have more bells and whistles on my new phase converter, like balancing and power factor correction caps, dual idlers, blah blah, but they do not change the basic fact that these motors are indeed parallel connected) On Wed, 4 Jan 2006 13:20:04 -0600, Robert Swinney wrote: Well, Don - you've missed the point again! What part of "2 induction motors operating from single phase current in a RPC configuration cannot be in parallel" did you fail to understand. Your well intentioned, and colorful, drawings were not of a RPC configuration. Draw out a RPC and I think you may understand. Oh! be sure to include some capacitors. They (in electronic terms) might be considered as steering capacitors, for it is their job to force the convoluted currents to flow in such a way as to *emulate* true 3-phase. Note, I said *emulate* because current flow in a RPC is not the same as current flow in parallel connected 3-phase motors, no matter which transform is used. Bob Swinney "Don Foreman" wrote in message ... On Wed, 4 Jan 2006 11:45:55 -0600, "Robert Swinney" wrote: Don, See my previous post, where I tried to show 2 induction motors operating from single phase current in a RPC configuration cannot be in parallel. I saw it. I just don't agree with it. See recent post showing things in 3D. Transform to Y using the usual Y-delta transforms if you like. See any textbook on the subject. In the Y case they don't look in parallel if there is no neutral connection. However, since a delta depiction clearly shows that they *ARE* in parallel, they are in freakin' parallel, BOB! Must I glue up some popsicle sticks for you? Can you explain the discrepancy? :) Hint: if there is no potential between unconnected points (the neutrals in a Y configuration) then they are effectively connected. Don "half-cocked" Foreman half cocked my arse....grumble mutter ....chuckle -- |
Flywheel on a rotary phase convertor
In article , Don Foreman says...
My RPC has no capacitors, starts and plug-reverses my lathe and mill just fine. Wait. Don and Jim.... separated at birth? :^) Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
Flywheel on a rotary phase convertor
In article , Robert Swinney says...
The only way the two 3-phase motors could be connected in parallel is if they are both fed from a 3-phase source. Ah, this *is* a semantic minefield. I think I see your point finally. They're not, and cannot be in parallel, if one thinks that being in parallel means they each have that extra wire there. The third leg doesn't, it's missing the extra external connection that the line wire represents. From a rough electrician's standpoint consider what the wiring looks like when I have my drum switch turned on at the lathe, but the converter is not energized at the knife switch on the wall. L1 and L2 are missing. There's no external current source so the third leg is now identical to all the others. At that point then they truly are in parallel - from an electrican's view as well as a EE's view. When the converter is operating of course there is one special lead that breaks the symmetry - it's missing the line connection. An electrican would say that the absence of that line connection does not change the fact the two sets of windings are in parallel. A EE looks at the entire network as a system, including the incoming power. He says parallel means all nodes have the same number of connections. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
Flywheel on a rotary phase convertor
jim rozen wrote:
In article , Robert Swinney says... The only way the two 3-phase motors could be connected in parallel is if they are both fed from a 3-phase source. Ah, this *is* a semantic minefield. I think I see your point finally. They're not, and cannot be in parallel, if one thinks that being in parallel means they each have that extra wire there. The third leg doesn't, it's missing the extra external connection that the line wire represents. From a rough electrician's standpoint consider what the wiring looks like when I have my drum switch turned on at the lathe, but the converter is not energized at the knife switch on the wall. L1 and L2 are missing. There's no external current source so the third leg is now identical to all the others. At that point then they truly are in parallel - from an electrican's view as well as a EE's view. When the converter is operating of course there is one special lead that breaks the symmetry - it's missing the line connection. An electrican would say that the absence of that line connection does not change the fact the two sets of windings are in parallel. A EE looks at the entire network as a system, including the incoming power. He says parallel means all nodes have the same number of connections. I'm glad I have VFD's and don't have to use so much brainpower figuring out how they work (: |
Flywheel on a rotary phase convertor
Well, you're reading a lot more into the Hanrahan drawing (conv/fig 1) than
I can see. Hanrahan didn't show the load motor, only assigned terminal numbers 1, 2 and 3 to it. I would have to assume he meant T1 and T2 on the idler went to windings 1 and 2 of the motor. And it would be a fair guess he intended for those same connections to go to windings 1 and 2 of the load motor; granted those would be in parallel. But T3 on the idler, let's call that an "outside" end of the winding for the sake of convention, goes to 3 on the load. Wouldn't it be a safe guess then that 3 on the load is an outside end of that coil also? I believe the confusion comes from the fact the 3rd leg is both source and load in a RPC instead of a single lead tied back to a common source as in a true parallel arrangement. Hey! You almost got it below, when you said, "because the third leg of the idler is a driving leg rather than a driven leg." The third leg is both a driver and a driven leg, plain and simple. The 3rd leg is a part of a complete network (mesh it if you like) and it cannot be separated into a generator only portion of the RPC. The RPC consists of an idler and a load with the 3rd leg serving as both generator and consumer - not server only as if it were a simple parallel connection. See the explanation given to Iggy, copied here for your convenience: ""Now look at the way current flows in the L3 lead. The idler's L3 wire has 1 end connected to the 3rd. winding on the idler, call that a source point for L3 current flow. The other end of wire L3 connects not to the analogous same start point on the load motor but to a point on the other end of the load motor's L3. This is not, can not, be considered a parallel connection. The only way the two 3-phase motors could be connected in parallel is if they are both fed from a 3-phase source. In a manner of speaking, for a RPC (network) to do its thing, when taking in *single-phase* current and delivering *3-phase current* to a load motor (also part of the network) there has to be current flow in 2 directions in the 3rd leg. Of course, aggregate current flow is such that current will flow in the "right" direction in the load motor's 3rd leg. Parts of the RPC act as both generators and consumers, thus the heavier element will cause current to flow, seemingly backwards, into the other element. And so it is with the RPC - capacitor augmentation can enhance the convoluted current flow in such a way as to make emulated 3-phase current flow in the load motor."" As for wizardry and witchcraft, I see none in the operation of a RPC, balanced or not. Try to embrace the idea of the 3rd leg as both generator and consumer, and you'll have less trouble when you try to mesh things out. I will leave the horrendous math up to you as you seem to have already figured it out. Bob Swinney "Don Foreman" wrote in message ... On Wed, 4 Jan 2006 13:20:04 -0600, "Robert Swinney" wrote: Well, Don - you've missed the point again! What part of "2 induction motors operating from single phase current in a RPC configuration cannot be in parallel" did you fail to understand. The part that disagrees with an acknowledged authority, Mr. Hanrahan: http://www.metalwebnews.com/howto/ph-conv/fig1.html Your well intentioned, and colorful, drawings were not of a RPC configuration. Draw out a RPC and I think you may understand. I did. So did Hanrahan. His are in parallel. http://www.metalwebnews.com/howto/ph-conv/fig1.html Oh! be sure to include some capacitors. He did. They (in electronic terms) might be considered as steering capacitors, for it is their job to force the convoluted currents to flow in such a way as to *emulate* true 3-phase. Note, I said *emulate* because current flow in a RPC is not the same as current flow in parallel connected 3-phase motors, no matter which transform is used. Convoluted currents? Yeesh! RPC's aren't witchcraft and wizardry, mesh currents are mesh currents. The (parallel) caps provide some phase correction and resonant voltage boost to compensate for the reversal in I-Z drop They are not essential to the operation of an RPC, though they can improve balance. My RPC has no capacitors, starts and plug-reverses my lathe and mill just fine. |
Flywheel on a rotary phase convertor
Jim sez"
Ah, this *is* a semantic minefield. ***I think I see your point finally.*** They're not, and cannot be in parallel, if one thinks that being in parallel means they each have that extra wire there. The third leg doesn't, it's missing the extra external connection that the line wire represents. From a rough electrician's standpoint consider what the wiring looks like when I have my drum switch turned on at the lathe, but the converter is not energized at the knife switch on the wall. L1 and L2 are missing. There's no external current source so the third leg is now identical to all the others. At that point then they truly are in parallel - from an electrican's view as well as a EE's view. When the converter is operating of course there is one special lead that breaks the symmetry - it's missing the line connection. An electrican would say that the absence of that line connection does not change the fact the two sets of windings are in parallel. A EE looks at the entire network as a system, including the incoming power. He says parallel means all nodes have the same number of connections. Jeeze, Jim! Thanks, I think. And just about when I pictured you with your ball cap turned around the right way and it said "Gary Coffman" on the bill. Bob Swinney |
Flywheel on a rotary phase convertor
In article , Robert Swinney says...
Jeeze, Jim! Thanks, I think. And just about when I pictured you with your ball cap turned around the right way and it said "Gary Coffman" on the bill. I always thought that gary's insights to matters like this (EE related) were typically very valid. And he was the one who suggested that flywheels probably hurt rather than help. I think that gary would see your "not really parallel" view of life and agree mostly. But honestly, whenever I have to tell somebody how to "make" a phase converter, they're typically electrically-savvy folks who want to run a machine. The easiest way to explain it to them is to say "you put the two idler motor leads across the line, and then you put the load motor smack dab in parallel with the idler leads. Basically there's a one-to-one correspondence between the leads of the idler and the load motor. No wires left over and all that sort of thing. Then they say "but what about the fact that the idler has the two incoming line leads hung on it?" and then I say "don't worry about those, the thing'll work just fine with them there." Red to red, black to black, blue to blue. Electricians like color codes. This is why I drive them crazy when I wire my motorcycles with all white wire. Makes drawing the diagram easy. "What color is *this* wire?" "White." Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
Flywheel on a rotary phase convertor
On 4 Jan 2006 13:22:13 -0800, jim rozen
wrote: When the converter is operating of course there is one special lead that breaks the symmetry - it's missing the line connection. An electrican would say that the absence of that line connection does not change the fact the two sets of windings are in parallel. A EE looks at the entire network as a system, including the incoming power. He says parallel means all nodes have the same number of connections. Jim He does? In circuit analysis, a set of two-terminal networks are regarded as "in parallel" if they are each connected to the same pair of nodes so the voltage across them is identically the same. Similarly, a set of n-terminal networks are in parallel if they are connected to the same set of n nodes so the various inter-terminal voltages on each n-terminal network are identically the same for corresponding pairs of terminals. This is regardless of whatever else might be connected to, between or among those nodes and regardless of any external symmetry or lack thereof. Some nodes may well have more connections than other. By this definition, if there are wires connecting each terminal of one device to a corresponding terminal of another device, they are in parallel -- regardless of what else might be connected to those terminals. |
Flywheel on a rotary phase convertor
On Wed, 4 Jan 2006 15:49:52 -0600, "Robert Swinney"
wrote: Well, you're reading a lot more into the Hanrahan drawing (conv/fig 1) than I can see. Hanrahan didn't show the load motor, only assigned terminal numbers 1, 2 and 3 to it. I would have to assume he meant T1 and T2 on the idler went to windings 1 and 2 of the motor. And it would be a fair guess he intended for those same connections to go to windings 1 and 2 of the load motor; granted those would be in parallel. But T3 on the idler, let's call that an "outside" end of the winding for the sake of convention, goes to 3 on the load. Wouldn't it be a safe guess then that 3 on the load is an outside end of that coil also? I believe the confusion comes from the fact the 3rd leg is both source and load in a RPC instead of a single lead tied back to a common source as in a true parallel arrangement. Hey! You almost got it below, when you said, "because the third leg of the idler is a driving leg rather than a driven leg." The third leg is both a driver and a driven leg, plain and simple. The 3rd leg is a part of a complete network (mesh it if you like) and it cannot be separated into a generator only portion of the RPC. The RPC consists of an idler and a load with the 3rd leg serving as both generator and consumer - not server only as if it were a simple parallel connection. The roles of "generator" and "server" just have to do with direction of current flow, in a parallel connection or otherwise. For example, the elements of a parallel-resonant circuit alternately act as energy source and energy sink. Even though they have the same voltage impressed across them, they may (usually do) have currents flowing in opposite directions. See the explanation given to Iggy, copied here for your convenience: ""Now look at the way current flows in the L3 lead. The idler's L3 wire has 1 end connected to the 3rd. winding on the idler, call that a source point for L3 current flow. The other end of wire L3 connects not to the analogous same start point on the load motor but to a point on the other end of the load motor's L3. This is not, can not, be considered a parallel connection. Why not? The only way the two 3-phase motors could be connected in parallel is if they are both fed from a 3-phase source. How they are (are aren't) fed by an external system does not change the way they are connected! "Parallel connection" is a matter of physical topology. In a manner of speaking, for a RPC (network) to do its thing, when taking in *single-phase* current and delivering *3-phase current* to a load motor (also part of the network) there has to be current flow in 2 directions in the 3rd leg. Of course, aggregate current flow is such that current will flow in the "right" direction in the load motor's 3rd leg. Parts of the RPC act as both generators and consumers, thus the heavier element will cause current to flow, seemingly backwards, into the other element. Yet it isn't a generator. Hmmm...... And so it is with the RPC - capacitor augmentation can enhance the convoluted current flow in such a way as to make emulated 3-phase current flow in the load motor." It's threephase with or without the capacitors, though the phases may be unbalanced with different-than-ideal phase relationships and magnitudes. The caps just improve balance under a given set of conditions. As for wizardry and witchcraft, I see none in the operation of a RPC, balanced or not. Try to embrace the idea of the 3rd leg as both generator and consumer, and you'll have less trouble when you try to mesh things out. I will leave the horrendous math up to you as you seem to have already figured it out. I think we each have things figured out, though clearly not in the same way. There are lots of ways to look at things. The concept of rotating fields is a fiction and an artifice, as is the practice of dealing with complex impedances using the (imaginary) square root of -1 as EE's are so fond of dong. There are lots of ways to think about what's going on. They aren't necessarily mutually exclusive. |
Flywheel on a rotary phase convertor
Sorry, Don. The lead between the 3rd leg terminals does not place them in
parallel with each other because it connects from one end of one winding to the *other* end of the other winding. Voltage symmetry and a parallel connection as commonly defined cannot exist under those conditions. By your definition below, the wire does not connect one terminal of one device to a corresponding terminal of the other device. Granted, the 2 line terminals do meet that criteria but the 3rd leg terminals do not. Thanx, Jim for taking Don by the hand and trying to help him out. I think he is getting there. At least he has come up with a plausible definition of "parallel". That's progress! Bob Swinney "Don Foreman" wrote in message ... On 4 Jan 2006 13:22:13 -0800, jim rozen wrote: When the converter is operating of course there is one special lead that breaks the symmetry - it's missing the line connection. An electrican would say that the absence of that line connection does not change the fact the two sets of windings are in parallel. A EE looks at the entire network as a system, including the incoming power. He says parallel means all nodes have the same number of connections. Jim He does? In circuit analysis, a set of two-terminal networks are regarded as "in parallel" if they are each connected to the same pair of nodes so the voltage across them is identically the same. Similarly, a set of n-terminal networks are in parallel if they are connected to the same set of n nodes so the various inter-terminal voltages on each n-terminal network are identically the same for corresponding pairs of terminals. This is regardless of whatever else might be connected to, between or among those nodes and regardless of any external symmetry or lack thereof. Some nodes may well have more connections than other. By this definition, if there are wires connecting each terminal of one device to a corresponding terminal of another device, they are in parallel -- regardless of what else might be connected to those terminals. |
Flywheel on a rotary phase convertor
"Don Foreman" wrote in message ... On Wed, 4 Jan 2006 15:49:52 -0600, "Robert Swinney" wrote: Well, you're reading a lot more into the Hanrahan drawing (conv/fig 1) than I can see. Hanrahan didn't show the load motor, only assigned terminal numbers 1, 2 and 3 to it. I would have to assume he meant T1 and T2 on the idler went to windings 1 and 2 of the motor. And it would be a fair guess he intended for those same connections to go to windings 1 and 2 of the load motor; granted those would be in parallel. But T3 on the idler, let's call that an "outside" end of the winding for the sake of convention, goes to 3 on the load. Wouldn't it be a safe guess then that 3 on the load is an outside end of that coil also? I believe the confusion comes from the fact the 3rd leg is both source and load in a RPC instead of a single lead tied back to a common source as in a true parallel arrangement. Hey! You almost got it below, when you said, "because the third leg of the idler is a driving leg rather than a driven leg." The third leg is both a driver and a driven leg, plain and simple. The 3rd leg is a part of a complete network (mesh it if you like) and it cannot be separated into a generator only portion of the RPC. The RPC consists of an idler and a load with the 3rd leg serving as both generator and consumer - not server only as if it were a simple parallel connection. The roles of "generator" and "server" just have to do with direction of current flow, in a parallel connection or otherwise. For example, the elements of a parallel-resonant circuit alternately act as energy source and energy sink. Even though they have the same voltage impressed across them, they may (usually do) have currents flowing in opposite directions. See the explanation given to Iggy, copied here for your convenience: ""Now look at the way current flows in the L3 lead. The idler's L3 wire has 1 end connected to the 3rd. winding on the idler, call that a source point for L3 current flow. The other end of wire L3 connects not to the analogous same start point on the load motor but to a point on the other end of the load motor's L3. This is not, can not, be considered a parallel connection. Why not? The only way the two 3-phase motors could be connected in parallel is if they are both fed from a 3-phase source. How they are (are aren't) fed by an external system does not change the way they are connected! "Parallel connection" is a matter of physical topology. Agreed! In a manner of speaking, for a RPC (network) to do its thing, when taking in *single-phase* current and delivering *3-phase current* to a load motor (also part of the network) there has to be current flow in 2 directions in the 3rd leg. Of course, aggregate current flow is such that current will flow in the "right" direction in the load motor's 3rd leg. Parts of the RPC act as both generators and consumers, thus the heavier element will cause current to flow, seemingly backwards, into the other element. Yet it isn't a generator. Hmmm...... And so it is with the RPC - capacitor augmentation can enhance the convoluted current flow in such a way as to make emulated 3-phase current flow in the load motor." It's threephase with or without the capacitors, though the phases may be unbalanced with different-than-ideal phase relationships and magnitudes. The caps just improve balance under a given set of conditions. No. A RPC is not a three-phase device in the classical sense; It isn't fed with 3-phases and it does not "generate" 3 phases as would, say a 3-phase alternator. True, the currents circulating in the load motor may make you think they are 3-phase but that is because they are the products of a special network. That network is *not* comprised of motors having all 3 sets of leads connected in parallel. Because of the way it is connected, that network has the capability of taking single-phase current into two 3-phase motors and delivering currents that emulates true 3 phase current. Key to accomplishing this is the non-parallel connection between the 3rd legs. Bob Swinney As for wizardry and witchcraft, I see none in the operation of a RPC, balanced or not. Try to embrace the idea of the 3rd leg as both generator and consumer, and you'll have less trouble when you try to mesh things out. I will leave the horrendous math up to you as you seem to have already figured it out. I think we each have things figured out, though clearly not in the same way. There are lots of ways to look at things. The concept of rotating fields is a fiction and an artifice, as is the practice of dealing with complex impedances using the (imaginary) square root of -1 as EE's are so fond of dong. There are lots of ways to think about what's going on. They aren't necessarily mutually exclusive. |
Flywheel on a rotary phase convertor
Suppose I take a three phase motor and use some method to get it
running on a single phase source, and then connect the three leads of the motor to a three phase rectifier bridge. Do I not have three phase power going to the rectifier bridge? Is my ripple current not pretty much what I would expect if I had the rectifier bridge connected to the output of a three phase generator? It seems to me that a RPC does not need a load motor to work. Dan Robert Swinney wrote: No. A RPC is not a three-phase device in the classical sense; It isn't fed with 3-phases and it does not "generate" 3 phases as would, say a 3-phase alternator. True, the currents circulating in the load motor may make you think they are 3-phase but that is because they are the products of a special network. That network is *not* comprised of motors having all 3 sets of leads connected in parallel. Because of the way it is connected, that network has the capability of taking single-phase current into two 3-phase motors and delivering currents that emulates true 3 phase current. Key to accomplishing this is the non-parallel connection between the 3rd legs. Bob Swinney |
Flywheel on a rotary phase convertor
On 4 Jan 2006 10:09:34 -0800, jim rozen
wrote: In article , Don Foreman says... The rotor field is always in space quadrature from the stator field. This is well-established in about any textbook on the subject. That being the case, the emf it induces in the third leg is necessarily in quadrature with the emf impressed by the line (and countered by the stator field) in the other two windings. I thought it was the rotor *current* that was in quadrature. It is. Same thing. Ampere's law. Field is proportional to current. |
Flywheel on a rotary phase convertor
On Wed, 4 Jan 2006 22:34:04 -0600, "Robert Swinney"
wrote: Sorry, Don. The lead between the 3rd leg terminals does not place them in parallel with each other because it connects from one end of one winding to the *other* end of the other winding. Ah, the *other* end of a three-terminal network. I have so much to learn! Voltage symmetry and a parallel connection as commonly defined cannot exist under those conditions. By your definition below, the wire does not connect one terminal of one device to a corresponding terminal of the other device. Granted, the 2 line terminals do meet that criteria but the 3rd leg terminals do not. There's only three freakin' terminals, there ain't no *other* end. Further, parallelism has no requirement of voltage symmetry. Parallelism, in conventional terms, is a matter of topology. Further, internodal voltages are what they are, however labelled, symmetrical or not, whether or not they match your expectations. Terminals connected together are nodes by definition -- in conventional terminology. If the labelling doesn't match then the labelling is wrong. The issue here may be "as commonly defined" as that doesn't match your theory. Progress he it's good to clarify where your theory deviates from common definition and conventional engineering terminology. Thanx, Jim for taking Don by the hand and trying to help him out. I think he is getting there. At least he has come up with a plausible definition of "parallel". That's progress! Yes, thanks Jim! I particularly like the idea of using all white wires. |
Flywheel on a rotary phase convertor
In article , Don Foreman says...
When the converter is operating of course there is one special lead that breaks the symmetry - it's missing the line connection. An electrican would say that the absence of that line connection does not change the fact the two sets of windings are in parallel. A EE looks at the entire network as a system, including the incoming power. He says parallel means all nodes have the same number of connections. He does? In circuit analysis, a set of two-terminal networks are regarded as "in parallel" if they are each connected to the same pair of nodes so the voltage across them is identically the same. WEll yes. I didn't say it was a conventional definition. I think electricians (and a good many other folks) will give a resounding huh? when exposed to it. But it's *internally* consistent. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
Flywheel on a rotary phase convertor
In article , Don Foreman says...
Yes, thanks Jim! I particularly like the idea of using all white wires. Cuts down on a lot of confusion, it does. g Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
Flywheel on a rotary phase convertor
Dan sez: "Suppose I take a three phase motor and use some method to get it
running on a single phase source, and then connect the three leads of the motor to a three phase rectifier bridge. Do I not have three phase power going to the rectifier bridge? Is my ripple current not pretty much what I would expect if I had the rectifier bridge connected to the output of a three phase generator? It seems to me that a RPC does not need a load motor to work." Yes, Dan (I think) you'd have 3-phase current going to the rectifier bridge. This is true by virtue of the fact a 3-phase motor running on single-phase delivers 3 phase currents to a resistive load. Notice, I did not say "generates" 3-phase current because the original single-phase line terminals are connected through to the resistive load and the other "phase", if you will, is derived via transformer action within the 3-phase motor. The 3rd. leg voltage, and current, into the rectifier will (obviously) be less than the single-phase line voltage suplied directly to the rectifier. Now, stop at this point and forget the rectifier. The description above would apply equally well if the load on the idler was composed of 3 light bulbs, also a resistive load. In that case, the light connected directly across the single-phase line would burn at full brilliance while the other 2 bulbs connected from the 3rd leg to L1 and L2 respectively would burn at less than full brilliance. IMO, your other point re. a RPC needing a load motor to work is moot. This because an idler motor alone is not a RPC. Bob Swinney wrote in message oups.com... Dan Robert Swinney wrote: No. A RPC is not a three-phase device in the classical sense; It isn't fed with 3-phases and it does not "generate" 3 phases as would, say a 3-phase alternator. True, the currents circulating in the load motor may make you think they are 3-phase but that is because they are the products of a special network. That network is *not* comprised of motors having all 3 sets of leads connected in parallel. Because of the way it is connected, that network has the capability of taking single-phase current into two 3-phase motors and delivering currents that emulates true 3 phase current. Key to accomplishing this is the non-parallel connection between the 3rd legs. Bob Swinney |
Flywheel on a rotary phase convertor
Again, taking some point another poster has made, as if it was his own, Iggy
bleats: "You are right, it does not need a load motor. You could run a resistive load (a 3 ph heater), or, like I do, a 3 phase welder that starts with a transformer and rectifier." Bob (does not suffer trolls) Swinney |
Flywheel on a rotary phase convertor
Sorry for taking some time to reply to this thread.
As Jim says, this does seem to be a semantic minefield. But I suspect that were people face-to-face they could hammer out their differences fairly quickly. It is often the way on Usenet. My take on the contentious issues is as follows. The idler motor will generate a voltage at the third terminal when not connected to a load, but it cannot supply any generated power because no current can be drawn. The difference here is between generated voltage and generated power. I would say that the RPC idler and load motors are in parallel in a topological sense. However, the current flow within the windings of the motors will be very different from what would be seen if the two motors were connected in parallel across a three phase supply. I suspect that this is the root of the disagreement here. All are fair points. Chris |
Flywheel on a rotary phase convertor
Don Foreman wrote:
snip My RPC has no capacitors, starts and plug-reverses my lathe and mill just fine. Out of interest, what are the horsepower ratings of your RPC idler and lathe and mill main motors? Chris |
Flywheel on a rotary phase convertor
Wayne Cook wrote:
On Tue, 3 Jan 2006 21:07:42 +0000 (UTC), Christopher Tidy wrote: I can't seem to find any used flywheels to fit my motor, but I can get a brand new flywheel for £40. I'm not sure if it is worth it in order to satisfy my scientific curiousity. If I get a different motor, I can get a flywheel for next to nothing, but that will involve lots of effort, bartering and deals in order to get a motor which isn't quite so cool. I won't touch the theoretical discussions on this thread. However I thought I might mention that if you wanted to experiment cheaply I'm sure you can find a used cast iron pulley in large enough diameter to serve as your flywheel. Preferably a multi-groove pulley. Thanks for that thought, Wayne. It actually entered my head a month or two ago, but for some reason I'd forgotten about it again. I have a couple of two-groove cast iron pulleys which fit this motor. Each weighs about 10 lb and is about 8" in diameter. I'm not sure if I can fit two on the shaft, but it'll certainly take one. It seems like there is no data regarding flywheels on RPC idlers. A few people have suggested that it may help with plug reversing (which is what I was thinking) but it seems unclear what the effect will be while the convertor is running in a steady state. My motor already has a pretty heavy rotor (about 8" diameter), but the energy stored will be reduced by the fact that it spins fairly slowly (940 rpm). My aim is to get the best performance out of a convertor with a limited idler size. If I get chance to experiment with a flywheel and acquire some data, I will. Thanks for all the input. Chris |
Flywheel on a rotary phase convertor
Christopher Tidy wrote (in part)...
The idler motor will generate a voltage at the third terminal when not connected to a load, but it cannot supply any generated power because no current can be drawn. I don't understand how it's possible by the laws of physics for both of these statements to be true. Jim |
Flywheel on a rotary phase convertor
Chris sez:
" I would say that the RPC idler and load motors are in parallel in a topological sense. However, the current flow within the windings of the motors will be very different from what would be seen if the two motors were connected in parallel across a three phase supply. I suspect that this is the root of the disagreement here." Well, how's that for getting at the crux of the biscuit, eh? Semantics are us! You display a depth of understanding that goes way past most of the arguments set forth in this thread. Your description, above, very aptly conveys a depth of appreciation for the manner in which currents must flow in a RPC. Perhaps in trying to describe those currents, my use of the term "convoluted" was an unwise choice. I suppose it was not "technically precise" enough for some of the intelligencia on RCM for they sought to jump on words and skip over any element of mutual comprehension. Apparently there was no "mutual comprehension" save for maybe Jim Rozen and yourself. Parallel was another bad choice of words - although it apparently had more technical appeal to those that demand precise engineering definition. Many of the respondents chose to pick on the absolute definition of "parallel" while totally overlooking the context in which it was used. Bob Swinney |
Flywheel on a rotary phase convertor
On Fri, 6 Jan 2006 07:56:15 -0700, Jim Wilson
wrote: Christopher Tidy wrote (in part)... The idler motor will generate a voltage at the third terminal when not connected to a load, but it cannot supply any generated power because no current can be drawn. I don't understand how it's possible by the laws of physics for both of these statements to be true. Jim I think he refers to a case where the third leg of the idler has no external connection; that terminal is just hangin' out in the breeze. It could still exhibit a voltage, but no current flows because there is no circuit in which it can flow. If no current flows thru that terminal , then no power is transferred into or out of it. |
Flywheel on a rotary phase convertor
On Fri, 6 Jan 2006 07:30:58 +0000 (UTC), Christopher Tidy
wrote: Don Foreman wrote: snip My RPC has no capacitors, starts and plug-reverses my lathe and mill just fine. Out of interest, what are the horsepower ratings of your RPC idler and lathe and mill main motors? Chris Idler is 5 HP. Lathe is 3 or 5 HP, mill is 1 HP. My idler runs the lathe just fine when the lathe is set to the 3HP setting, but can't quite hack it on the 5 HP setting. If I needed the higher speeds (2x) of the 5 HP setting, I'd probably need a bit larger idler. It might pull it if it were a belt-drive lathe or had a clutch, but it's a gearhead lathe. It tries to work on the 5 HP setting, but it blows the breaker in the lathe before it can get wound up to speed. Adding some capacitors probably would help some, but I think a bigger idler would be the best solution. I'm content to use it as is. 1000 RPM is fast enough to do everything I want to do on that lathe. The 1 HP mill has no problem operating at any speed. Smaller motor, less inertia. |
Flywheel on a rotary phase convertor
In article , Don Foreman says...
On 4 Jan 2006 10:09:34 -0800, jim rozen wrote: In article , Don Foreman says... The rotor field is always in space quadrature from the stator field. This is well-established in about any textbook on the subject. That being the case, the emf it induces in the third leg is necessarily in quadrature with the emf impressed by the line (and countered by the stator field) in the other two windings. I thought it was the rotor *current* that was in quadrature. It is. Same thing. Ampere's law. Field is proportional to current. Ah, hang on there. The field in the rotor has to be 180 degrees out from the stator fields, from Lenz's law, right? Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
Flywheel on a rotary phase convertor
Robert Swinney wrote:
Chris sez: " I would say that the RPC idler and load motors are in parallel in a topological sense. However, the current flow within the windings of the motors will be very different from what would be seen if the two motors were connected in parallel across a three phase supply. I suspect that this is the root of the disagreement here." Well, how's that for getting at the crux of the biscuit, eh? Semantics are us! You display a depth of understanding that goes way past most of the arguments set forth in this thread. Well, I had the benefit of reading all your posts before I wrote a response! Thanks for the compliment. I'm cleaning and painting the idler at the moment. Should be looking at a first test run as soon as I've wound a new secondary to provide 240 V - 415 V conversion. Best wishes, Chris |
Flywheel on a rotary phase convertor
Don Foreman wrote:
On Fri, 6 Jan 2006 07:56:15 -0700, Jim Wilson wrote: Christopher Tidy wrote (in part)... The idler motor will generate a voltage at the third terminal when not connected to a load, but it cannot supply any generated power because no current can be drawn. I don't understand how it's possible by the laws of physics for both of these statements to be true. Jim I think he refers to a case where the third leg of the idler has no external connection; that terminal is just hangin' out in the breeze. It could still exhibit a voltage, but no current flows because there is no circuit in which it can flow. If no current flows thru that terminal , then no power is transferred into or out of it. That's exactly what I meant. Chris |
Flywheel on a rotary phase convertor
Don Foreman wrote:
On Fri, 6 Jan 2006 07:30:58 +0000 (UTC), Christopher Tidy wrote: Don Foreman wrote: snip My RPC has no capacitors, starts and plug-reverses my lathe and mill just fine. Out of interest, what are the horsepower ratings of your RPC idler and lathe and mill main motors? Chris Idler is 5 HP. Lathe is 3 or 5 HP, mill is 1 HP. My idler runs the lathe just fine when the lathe is set to the 3HP setting, but can't quite hack it on the 5 HP setting. If I needed the higher speeds (2x) of the 5 HP setting, I'd probably need a bit larger idler. It might pull it if it were a belt-drive lathe or had a clutch, but it's a gearhead lathe. It tries to work on the 5 HP setting, but it blows the breaker in the lathe before it can get wound up to speed. Adding some capacitors probably would help some, but I think a bigger idler would be the best solution. I'm content to use it as is. 1000 RPM is fast enough to do everything I want to do on that lathe. The 1 HP mill has no problem operating at any speed. Smaller motor, less inertia. Thanks for those figures. All more data to add to the thought "melting pot". Chris |
Flywheel on a rotary phase convertor
Dan sez:
" In my opinion you need to realize that a RPC is an induction generator." Dan, I know you have some experience with induction generators so I'll ask you to respectfully consider that: An induction motor is a consumer, not a generator. As you know true induction generators (induction motors) have to be excited by overdrive from the AC mains in order to generate. Tht is not done in any fashion in a RPC. The RPC is a load on the mains, not a supplier to the mains. Again, I'll say, we need lose the idea of a RPC being a generator. Think of it as more of a converter; well, that's part of it's name now isn't it? Bob Swinney wrote in message oups.com... Robert Swinney wrote: IMO, you need to lose the thinking of a RPC as being a form of generator. Bob Swinney As far as flywheels are concerned, a flywheel will keep the slip angle from changing as quickly. So a RPC without a flywheel will draw power from the mains more quickly when the load is increased. Score points for that side. On the other hand, a RPC with a flywheel will draw power from the flywheel when the load is increased as well as from the mains. So score points for the other side. In the real world, it does not make much difference as the change in speed of the RPC should be slight, and therefore only a small amount of power can be drawn from the flywheel. Having a flywheel would help with an undersized RPC when the load motor is plugged. Dan |
Flywheel on a rotary phase convertor
On 6 Jan 2006 10:27:22 -0800, jim rozen
wrote: In article , Don Foreman says... On 4 Jan 2006 10:09:34 -0800, jim rozen wrote: In article , Don Foreman says... The rotor field is always in space quadrature from the stator field. This is well-established in about any textbook on the subject. That being the case, the emf it induces in the third leg is necessarily in quadrature with the emf impressed by the line (and countered by the stator field) in the other two windings. I thought it was the rotor *current* that was in quadrature. It is. Same thing. Ampere's law. Field is proportional to current. Ah, hang on there. The field in the rotor has to be 180 degrees out from the stator fields, from Lenz's law, right? I was vague, sorry. I meant rotor current. Rotor field (the field the rotor produces) is in phase with rotor current by Ampere's law relating magnetic field to current. That field is produced by rotor current resulting from EMF induced in the rotor by rate of change of stator field linking it -- Lenz's law, as you say. Rotor current is then this EMF / rotor_impedance. The rate of change is at slip speed -- stator flux rotates at synch speed, rotor rotates at slip rpm below synch speed. This is from the perspective of an observer on the rotor, using the artifice of rotating fields of constant magnitude to represent sinusoidally varying fields in space quadrature. The equivalance is mathematically correct, and a convenient way to look at things. It isn't the only way to look at things by any means, but I find it easiest to visualize. Reference: "Electric Machinery", Fitzgerald & Kingsley, McGraw Hill. Rotor field and stator field can be dealt with separately and independently, as when resolving vectors into components. They differ in phase because induced voltage in the rotor is the time derivative of stator flux apparently rotating at slip speed. They are usually very nearly in quadrature because the rotor impedance looks primarily resistive to rotor emf induced at slip frequency. Slip frequency is typically about 2.5 Hz at rated speed so rotor self-reactance is negligable. |
Flywheel on a rotary phase convertor
Sorry, Dan - Make that overdrive via overspeed from the prime mover to make
an induction generator. The induction generator (one made from a common induction motor) will generate when excited by the mains and when its rotor is driven by external means to a speed exceeding that of the motor's synchronous speed. Slip is said to be negative under these conditions. Bob Swinney "Robert Swinney" wrote in message ... Dan sez: " In my opinion you need to realize that a RPC is an induction generator." Dan, I know you have some experience with induction generators so I'll ask you to respectfully consider that: An induction motor is a consumer, not a generator. As you know true induction generators (induction motors) have to be excited by overdrive from the AC mains in order to generate. Tht is not done in any fashion in a RPC. The RPC is a load on the mains, not a supplier to the mains. Again, I'll say, we need lose the idea of a RPC being a generator. Think of it as more of a converter; well, that's part of it's name now isn't it? Bob Swinney wrote in message oups.com... Robert Swinney wrote: IMO, you need to lose the thinking of a RPC as being a form of generator. Bob Swinney As far as flywheels are concerned, a flywheel will keep the slip angle from changing as quickly. So a RPC without a flywheel will draw power from the mains more quickly when the load is increased. Score points for that side. On the other hand, a RPC with a flywheel will draw power from the flywheel when the load is increased as well as from the mains. So score points for the other side. In the real world, it does not make much difference as the change in speed of the RPC should be slight, and therefore only a small amount of power can be drawn from the flywheel. Having a flywheel would help with an undersized RPC when the load motor is plugged. Dan |
Flywheel on a rotary phase convertor
On Fri, 6 Jan 2006 16:43:51 -0600, "Robert Swinney"
wrote: Dan sez: " In my opinion you need to realize that a RPC is an induction generator." Dan, I know you have some experience with induction generators so I'll ask you to respectfully consider that: An induction motor is a consumer, not a generator. As you know true induction generators (induction motors) have to be excited by overdrive from the AC mains in order to generate. Tht is not done in any fashion in a RPC. The RPC is a load on the mains, not a supplier to the mains. Again, I'll say, we need lose the idea of a RPC being a generator. Think of it as more of a converter; well, that's part of it's name now isn't it? Bob Swinney A fella by the name of Swinney said elsewhere that idler and load motor function both as generators and loads. True statement. Emf is produced in all three windings of the idler. In the driven windings, those connected to the mains, that emf is slightly less than applied voltage so the current in those windings is (Vline - Vemf)/Zwnding. A similar but phase-displaced emf is also produced in the third leg. This emf can then drive (supply power to) the third leg of the load motor which also is not connected to the mains. So neither the idler nor the load are generators from the perspective of the mains, but the idler, regardless of what else you may call it, does supply current and power to the load motor's third leg. I would therefore argue that the idler alone is a rotary phase converter (RPC) because it produces a voltage on its third leg that is of different phase from the mains voltage whether or not it has a load connected to it. It isn't a rotary power converter (also RPC) unless there is a load connected, because if there is no load connection then the idler's third leg has no current so there is no different-phase power. In either case, this different phase is not exactly right in magnitude or phase to make the result balanced threephase, though if the idler is big enough (low impedance) it'll be pretty close. This is because the IZ drops in the driven windings of the idler are different in polarity wrt the emf than is the case in the third leg. The discrepancy can be reduced with capacitors, at least for a particular load motor and particular mechanical or useful load. |
Flywheel on a rotary phase convertor
In article , Don Foreman says...
Rotor field and stator field can be dealt with separately and independently, as when resolving vectors into components. They differ in phase because induced voltage in the rotor is the time derivative of stator flux apparently rotating at slip speed. They are usually very nearly in quadrature because the rotor impedance looks primarily resistive to rotor emf induced at slip frequency. ... OK, makes sense to me. Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
Flywheel on a rotary phase convertor
In article , Don Foreman says...
I would therefore argue that the idler alone is a rotary phase converter (RPC) because it produces a voltage on its third leg that is of different phase from the mains voltage whether or not it has a load connected to it. It isn't a rotary power converter (also RPC) unless there is a load connected, because if there is no load connection then the idler's third leg has no current so there is no different-phase power. But, but, but. No tune capacitors. No pf correction. No potential relay or starting capacitors. No contactors, no control transformers. It can't *possibly* work. These things have to be complicated. http://www.metalworking.com/DropBox/_2000_retired_files/Conv.jpg Pardon me, I have to go make some chips... g Jim -- ================================================== please reply to: JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com ================================================== |
Flywheel on a rotary phase convertor
Don sez:
" A fella by the name of Swinney said elsewhere that idler and load motor function both as generators and loads. True statement." Yeah, But! That's not quite how I said it. I believe I said elements of a RPC function as both generators and consumers because of the way current flows in an entire RPC, not just in the idler motor. Don, dig out the little paper I sent you a couple of years ago and in there you will see some diagrams describing current flow in a RPC - an entire RPC; You do still have that little paper, don't you? Naw! I suppose not or else you wouldn't have slipped into the Iggy school of RPC's. Bob Swinney |
Flywheel on a rotary phase convertor
This may be going out on a limb, and if so, I'm quite sure Don is ready with
a saw but here goes: When I said: "Sorry, Don. The lead between the 3rd leg terminals does not place them in parallel with each other because it connects from one end of one winding to the *other* end of the other winding. " This concept was immediatly poo-pooed by the "if its connected as a RPC, then it is in parallel". Later, then a definition of parallel was given as: "By this definition, if there are wires connecting each terminal of one device to a corresponding terminal of another device, they are in parallel -- regardless of what else might be connected to those terminals." Consider 2 wye motors connected as a RPC, seemingly in parallel. It appears to me that 2 wye motors connected in parallel by the definition of corresponding terminals, above, are not in parallel by that definition unless the "star" or neutral points within each motor are connected by a solid lead. Then, all corresponding points are connected. RPC connected motors do not meet the criteria. Kapeesh? Bob (getting tired of all this)Swinney |
Flywheel on a rotary phase convertor
On Fri, 6 Jan 2006 20:12:59 -0600, "Robert Swinney"
wrote: Don sez: " A fella by the name of Swinney said elsewhere that idler and load motor function both as generators and loads. True statement." Yeah, But! That's not quite how I said it. I believe I said elements of a RPC function as both generators and consumers because of the way current flows in an entire RPC, not just in the idler motor. OK, but what does that mean? Currents in an entire anything flow thru the elements that comprise it, so current flow(s) in an entire RPC must flow thru its elements. The idler and the load motor are elements, are they not? Do you mean RPC to connote rotary phase converter? Do you assert that an RPC must have capacitors to be called an RPC? Is it the capacitors that function as both generators and loads? Don, dig out the little paper I sent you a couple of years ago and in there you will see some diagrams describing current flow in a RPC - an entire RPC; You do still have that little paper, don't you? Naw! I suppose not or else you wouldn't have slipped into the Iggy school of RPC's. Naw, I suppose not. I recall it, but I don't seem to have it on either computer. If it was paper, I certainly no longer have it. I must say I respect Iggy's rather consistent practice of courteous and civil discourse. |
Flywheel on a rotary phase convertor
On Wed, 4 Jan 2006 15:02:28 -0600, "Robert Swinney"
wrote: The key point here is: "How my phase converter is wired when it runs a load motor". The flawed logic is that a phase converter does not "run" a load motor. Such a differentiation between phase converter and load motor is not possible. An idler motor and load motor, taken together as a network, are what constitutes a rotary phase converter. This all harks back to the misunderstood "generator" concept as applied to an idler motor. The two must work together to form a rotary phase converter. Remember a RPC (the whole RPC) acts to manipulate current flow in a network so that the load motor voltages, and currents, are the same as if the load motor was operating from a 3-phase source. Remembering, all the while, the whole thing is running on *single-phase* current. Now as for parallel connectivity: The drawing is that of a classic RPC (idler and load motor) operating from Hot 1 and Hot 2, both sides of a single-phase source. Consider Hot 1. It connects to L1 of the idler motor and also to L1 of the load motor. The same can be said for Hot 2 and the 2 respective L2's. By definition, the points designated as L1 and L2 in both idler and load are operated in parallel across the line. That is to say the 2 main windings, L1 to L2 in your drawing of both idler and load are connected in parallel across the line. Now look at the way current flows in the L3 lead. The idler's L3 wire has 1 end connected to the 3rd. winding on the idler, call that a source point for L3 current flow. The other end of wire L3 connects not to the analogous same start point on the load motor but to a point on the other end of the load motor's L3. What "other end"? Nobody rewound the motor. It connects to the same terminal that motor came with. This is not, can not, be considered a parallel connection. The only way the two 3-phase motors could be connected in parallel is if they are both fed from a 3-phase source. They are connected in parallel regardless of how they are fed. The locus of confusion may be this: if you consider a Y connection, the third legs are in series with each other, though the three-terminal networks (idler and load motor) are connected in parallel. The function of an RPC is to make the voltage on L3 resemble the voltage of a third mains line in phase and magnitude if one were present. In a manner of speaking, for a RPC (network) to do its thing, when taking in *single-phase* current and delivering *3-phase current* to a load motor (also part of the network) there has to be current flow in 2 directions the 3rd leg. There's current flow in both directions everywhere in an AC system. If you meant to say power flow, I disagree. Power flows from idler third leg to load motor third leg. Net power over each cycle in L3 is, by definition for RPC function, flowing into the load same as it is on the other two lines just as would be the case if an actual third mains line of different phase were feeding L3 and the load motor. There will be some reactive component and power factor in all three legs, but they won't be greatly different from each other in an RPC that is working well. I agree that the RPC must be treated as a system to get the voltage on L3 to be right, because that voltage is determined by the idler, the load motor and any capacitances that are present. Another confusion factor is that the system is driven by "single" phase. How d'ya get three phases with one more wire? The trick to undestanding this is to regard the 220 mains as 110v and 110v180 (180 out of phase with the first line) either side of a neutral which may or may not actually exist as it does in the US and Canada. That can be viewed as being produced by two vectors of 127 volt magnitude with phase difference of 120 degrees. Let's take a snapshot in time where these vectors are at 120 and 240 degrees. The resulting line-to-line voltage is 220, though the unconnected neutral is now non-zero and in quadrature with the actual mains voltages, a voltage vector at 0 degrees in our snapshot. The third leg in the idler, referred to neutral in in a Y- connected motor, produces additional quadrature voltage, at 0 degress in our snapshot, as described in another post. If the magnitude and phase of the idler's third-leg contribution is just right, the resulting voltages on L1, L2 and L3 will look like balanced threephase mains. The contribution of the third leg will never be "just right", hence the addition of capacitors to adjust phase and magnitude as they resonate with the various inductive reactances in the system. Of course, aggregate current flow is such that current will flow in the "right" direction in the load motor's 3rd leg. What is aggregate current flow? Average current flow in any AC circuit is zero. Parts of the RPC act as both generators and consumers, Which parts? thus the heavier element will cause current to flow, seemingly backwards, into the other element. And so it is with the RPC - capacitor augmentation can enhance the convoluted current flow What does "convoluted current flow" mean? Convoluted compared to what? Even if the earnest reader deduces that the context is "intricate, complex, labyrinthine" rather than "rolled in a coil", it doesn't add a bit to his understanding of how an RPC works. Guys of our age, training and experience should be teaching what we know, Bob. I'd like to see a higher standard of contribution from you than I might expect from some others. I I think you know a lot but I think you could do a lot better job of teaching. Being tall enough to skip derision of readers who respectfully (or otherwise) disagree or "don't yet get it" wouldn't hurt a bit. in such a way as to make emulated 3-phase current flow in the load motor. Bob Swinney I think you have the general ideas right, but I really doubt that someone who didn't already have some understanding of how these things work would be helped by your explanation. Further, it's not right and not at all contributive to deride others who don't comprehend what you meant rather than what you said. "Ignoramus18299" wrote in message . .. Here's how my phase converter is wired when it runs a load motor: idler Load L3-------------------------L3 / \ / \ L1 --- L2 L1---L2 | | | | | +------------------------+ +-----------------------------+ Hot2 Hot1 L1 connected to L1, L2 connected to L2, L3 connected to L3. L1 and L2 are also connected to utility power Hot1 and Hot2. How are these motors not running in parallel? They are. Leg numbering on the load motor is somewhat arbitrary, but however these motors are connected, the poles are connected in parallel. Maybe you have a different definition of "connected in parallel". My definition is that potential between like points (L1 to L1, L2 to L2, L3 to L3) is zero. Current does flow from L3 of one motor to L3 of another. i (now I have more bells and whistles on my new phase converter, like balancing and power factor correction caps, dual idlers, blah blah, but they do not change the basic fact that these motors are indeed parallel connected) On Wed, 4 Jan 2006 13:20:04 -0600, Robert Swinney wrote: Well, Don - you've missed the point again! What part of "2 induction motors operating from single phase current in a RPC configuration cannot be in parallel" did you fail to understand. Your well intentioned, and colorful, drawings were not of a RPC configuration. Draw out a RPC and I think you may understand. Oh! be sure to include some capacitors. They (in electronic terms) might be considered as steering capacitors, for it is their job to force the convoluted currents to flow in such a way as to *emulate* true 3-phase. Note, I said *emulate* because current flow in a RPC is not the same as current flow in parallel connected 3-phase motors, no matter which transform is used. Bob Swinney "Don Foreman" wrote in message ... On Wed, 4 Jan 2006 11:45:55 -0600, "Robert Swinney" wrote: Don, See my previous post, where I tried to show 2 induction motors operating from single phase current in a RPC configuration cannot be in parallel. I saw it. I just don't agree with it. See recent post showing things in 3D. Transform to Y using the usual Y-delta transforms if you like. See any textbook on the subject. In the Y case they don't look in parallel if there is no neutral connection. However, since a delta depiction clearly shows that they *ARE* in parallel, they are in freakin' parallel, BOB! Must I glue up some popsicle sticks for you? Can you explain the discrepancy? :) Hint: if there is no potential between unconnected points (the neutrals in a Y configuration) then they are effectively connected. Don "half-cocked" Foreman half cocked my arse....grumble mutter ....chuckle -- |
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